The present invention relates generally to computer systems, and more particularly to power management systems for portable computer systems.
Computerized personal organizers are becoming increasingly popular with a large segment of the population. Computerized personal organizers tend to be small, lightweight, relatively inexpensive, and are able to perform such functions as keeping a calendar, an address book, a to-do list, etc. While many of these functions can also be provided in conventional computer systems, personal organizers are very well suited to the personal organization task due to their small size and portability. Computerized personal organizers are available from such companies as Sharp and Casio of Japan.
A relatively new form of computer, the pen-based computer system, holds forth the promise of a marriage of the power of a general purpose computer with the functionality and small size of a computerized personal organizer. A pen-based computer system is typically a small, hand-held computer where the primary method for inputting data includes a "pen" or stylus. A pen-based computer operating as personal organizer or "Personal Digital Assistant" (PDA) is made by Apple Computer, Inc. of Cupertino, Calif. under the trademark Newton.TM..
The aforementioned functionality of the PDA often requires a lengthy, elaborate start-up procedure. Start-up procedures for a PDA include both hardware and software initializations. Representative hardware start-up procedures include initializing the display screen, the writing tablet, and the system controller, turning power on to and initializing all other peripheral devices, and initializing all system memory. Representative software start-up procedures include building the memory management unit (MMU) tables in system memory, enabling the MMU on the CPU, and starting the operating system.
In addition to start-up procedure requirements, the PDA has unique shut-down requirements. For a PDA, or any computer system, to start-up efficiently, the system must begin from a known state. The start-up is therefore facilitated by an orderly shut-down. Furthermore, the PDA is typically a battery powered device, leaving it especially susceptible to abnormal shut-down conditions in circumstances such as battery failure or when replacing the battery. Thus it is important that memory management and initialization procedures during start-up and shut-down be more sophisticated than in the case of a desk top computer. This sophistication is perhaps a prerequisite for providing the user of a PDA with the expected level of functionality. For example, the PDA should provide key features of the non-electric organizer such as high data integrity and nearly immediate operation access.
From a simplistic view, an on/off switch of a PDA appears to simply switch the system between two states: power supply on and power supply off. But, as is well know to those skilled in the art of computer system design, the typical on/off switch has no direct effect on the power supply of the computer system. Rather, enabling and disabling the on/off switch respectively generate a power-up interrupt and a power-down interrupt within the system. The system responds to the interrupt with a predefined start-up or shut-down procedure, where start-up places the system in an activated state, and shut-down places the system in a non-activated state. It should be appreciated that the non-activated state does not correspond to a zero power-use state, but rather a low power-use state.
In most personal computer systems, when a user turns the on/off switch on, the system responds by performing what is known as a "cold boot" start-up procedure. The cold boot includes the steps required to initially start-up the computer system. As the functionality of the system grows, the time delay of the cold boot can become very undesirable. It should be appreciated that minimizing this delay is critical in the case of the PDA, as the PDA should be approximately as time economical as the non-computerized organizer.
While all of steps of the cold boot may be performed on start-up, the cold boot may include steps which are unnecessary. For example, initializing the display and the digitizing tablet need only occur once initially on the PDA, and thereafter only if an abnormal event has occurred. If an orderly shut-down occurred previously the start-up could skip many of these steps, thereby reducing the start-up time significantly.
Additionally, many of the software initialization steps, while required even after a previous orderly shut-down, are simply repetitive steps performed on each start-up. Page tables of the Newton PDA, which provide structure to the memory, must be rebuilt on each start-up. Any application software or peripheral devices which utilize volatile memory must completely rebuild in memory-on each start-up. The operating system often utilizes volatile memory which must be loaded on start-up. The MMU of the Newton PDA and the volatile memory is then updated to reflect the data in memory, which applications are running, and the location and status of the peripherals. Any process which eliminates or reduces the time required for these steps enhances the system.
Prior solutions to the time delay took advantage of knowing that a previous orderly shut-down would leave the computer system in a well defined state. This enabled a normal, "quick boot", start-up procedure which eliminated some of the unnecessary cold boot steps. This decreased, and thereby improved, the typical start-up time. However, these solutions created one problem while not solving another: if a previous shut-down was non-orderly, then the user had to manually force a cold boot start-up, either by disconnecting the power source or by engaging a cold boot button. Depending on the shut-down procedure, valuable user data could be lost.